Power to a new annex

Joined
19 Jun 2005
Messages
10
Reaction score
0
Country
United Kingdom
I am having a garage built and am toying with the idea of whether to add a little one bed annex also. For my own piece of mind I thought I'd enquire what the best method of getting power to this new building would be.

The requirements:
1 ringmain, 1 lighting radial & 1 shower (10.8kW) radial,

I prosume, maybe incorrectly thats why I'm asking, that it would require 16mm SWA (6942X) which is rated at 110A. What correction factors are required for direct burial :?:
Are there any other requirements apart from buried 500mm and warning tape at 150mm

This cable will supply CU protected by 80A 30mA RCD
Ringmain: 2.5mm T&E on 32A MCB
Lighting Radial: 1.5mm T&E on 6A MCB
Shower: 10mm T&E on 50A MCB
Are these calculations correct :?:



How would the 16mm SWA get its power, would the local electricity board have to come and put service connectors in for this cable :?:

Any help would be warmly welcomed :D
 
Sponsored Links
SWA is fine for direct burial. it should be burried in stone-free material to prevent damage to the cable from stones (probablly not a huge issue in practice but it is what the regs say). some sparkys preffer to use sand rather than soil as an extra warning to anyone who is digging and missed the marker tape that something is burried under there.

as for the size of the cable that depends on the distance (due to volt drop issues). probablly the best way to feed the cable is from a seperate 60A or 100A metalclad switchfuse connected to the tails by henlys (which is something that we don't reccomend diyers to do because it involves pulling the service fuse to isolate)

also you should consider possiblly overloading of your houses supply as a whole particularlly if you already have an electric shower.
 
which is something that we don't reccomend diyers to do because it involves pulling the service fuse to isolate

What is the normal routine for this. Do you request they come and pull it for you and then get them to seal it when you've done the work.

My service fuse has no seals on it, never has
 
in theory you are supposed to get the REC/DNO out to disconnect and reconnect. in practice many sparkys just pull the fuse themselves and unless you are actually stealing leccy its very unlikely that any action will be taken over this.

if you do decide to do it yourself (which we don't reccomend) then the following points should be borne in mind

1: if it looks in any way old/damaged DO NOT mess with it.
2: make sure consumer unit/switchfuse isolators are off both when pulling and when re-inserting pulling or re-inserting live can cause arcing.
3: make sure you don't touch the pins of the fuseholder when pulling.
4: look at the base after removing the fuseholder and if there is a lot of exposed metal cover it up with something to prevent accidental touching.
 
Sponsored Links
Yes its like calling a vacuem cleaner a Hoover, Henley is a brand name.
 
Obviously Building Control will be involved anyway - what's your particular one's approach to certifying DIY electrical work? Will you be DIYing it? (TIP - they are not allowed to charge you any extra on top of their normal fee associated with the building work - everything should be included)
 
Ban:
they are not allowed to charge you any extra on top of their normal fee associated with the building work - everything should be included)

Can you expand on this a little bit please, or point me in the direction of the topic, are you saying that Building control have an imposed limit to what they can charge for inspection? What about when only electrical work is involved?
 
ban-all-sheds said:
Obviously Building Control will be involved anyway - what's your particular one's approach to certifying DIY electrical work? Will you be DIYing it? (TIP - they are not allowed to charge you any extra on top of their normal fee associated with the building work - everything should be included)

So the inspector during his visit would inspect all electrical work as well as building and not charge any extra?

Surely if this is the case I could do the install, certify it myself and get buildng control to inspect it, therfore no need for a sparky at £25 Perhr

RESULT :D
 
So the story so far:

The requirements:
1 ringmain, 1 lighting radial & 1 shower (10.8kW) radial,

16mm SWA (6942X) which is rated at 110A.
buried 500mm and warning tape at 150mm

This cable will supply CU protected by 80A 30mA RCD
Ringmain: 2.5mm T&E on 32A MCB
Lighting Radial: 1.5mm T&E on 6A MCB
Shower: 10mm T&E on 50A MCB

16mm SWA supplied from Henlys through a 80A Metalclad DP Isolator

My existing CU RCD is 100A

100A(Existing CU) + 80A(Annex CU) = 180A
Service Fuse = 100A =

PROBLEM 1

If there is potential to load the mains at 180A how would I approach the fact that my service is rated at 100A

I know in reality I will never hit 180A, only under fault conditions but do I have to get my service uprated to cope with the extra load, 3 phase maybe with 1 phase for existing CU and 1 phase for Annex CU

Or can the service fuse be uprated?

Or can I use the common sense approach?

PROBLEM 2

The 16m SWA supplying my Annex would be 2core with the SWA used as CPC.
How would I terminate the earth at the gland as to be able to continue the CPC onto the existing Earthing system?

This is getting very confusing but it would be a lot worse without this forum
 
generally you should have your own overcurrent protection for undeground cable runs i'd reccomend a 60A metalclad switchfuse.

i'd also use a metalclad CU in the annex (terminating armoured in plastic boxes can be a pain)

as for overloading the main property supply i wouldn't worry too much. service fuses tend to be fairly slow to blow at moderate overloads and although showers draw a lot of current they don't do it for very long. i honestly wouldn't worry about this unless it starts blowing at which point you would need to talk to your rec/dno about upgrade options (and the option they give you will probablly be 3 phase)

all SWA should be terminated using the proper glands to earth the armour. generally i reccomend using 3 core with an extra core for earth as well to make sure the earth path stays sound and keep the earth fault loop impedance low.
 
alertelec said:
Can you expand on this a little bit please, or point me in the direction of the topic, are you saying that Building control have an imposed limit to what they can charge for inspection? What about when only electrical work is involved?
All the LABCs I've looked at have a schedule of charges for fees which are based on the value of the works. And that fee is supposed to cover all of their activities associated with Building Control for the works in question.

transducer said:
So the inspector during his visit would inspect all electrical work as well as building and not charge any extra?
Some LABCs (most, in fact) find themselves unable to carry out their own inspection & testing. Well - they only had 2 years and 3 months to prepare for their new responsibilities to check notified work for compliance with the Building Regulations....

Many of the LABCs that don't have the ability to do it themselves are exploiting the ignorance of their customers and indulging in sharp practice:

1) Charging people extra because they have chosen to subcontract electrical inspection and testing to a 3rd party. LABC Services, the umbrella organisation, have confirmed to me that LABCs are not allowed to do this. I recently asked them what the position was regarding LABCs charging extra because they had to subcontract, and this was the answer I received:

Building Regulation fees are set to a scale that embraces the whole scope of what may be necessary in respect of checking and approving the plans and inspecting the work. The input necessary can vary according to the circumstances of a specific scheme, but the fees are not variable due to this feature.

The local authority has a legal duty to carry out the Building Regulation function to a proper degree. This can also vary in extent according to the demands of any scheme and considerable discretion rests with the authority. However they are responsible to give a proper service within the fee and cannot charge extra for the reason you mention. Indeed if they failed to inspect yet still charged you might have a case for a refund.



2) Insisting that non-registered people themselves get the work inspected and tested by someone they regard as competent - it is quite clear that the legislation does not allow them to do this.

Surely if this is the case I could do the install, certify it myself and get buildng control to inspect it, therfore no need for a sparky at £25 Perhr
Yes you can. What happens then, vis-a-vis your Building Inspector's acceptance of the certificate will be interesting. A lot will depend on how reasonable he is, and on how much you are prepared to rock the boat.

If they want to charge you extra, you may have to fight hard to get them to accept that they can't and that the fee you paid them must cover the lot.

If they won't accept your certificate, and insist on one from an electrician, you're going to have to show that you have good grounds for believing that you are competent to issue it, and you are going to have to argue with them over the fact that the law does not give them the power to insist on a certificate from someone else and also that neither the law, nor the IEE Wiring Regulations (which are not mandatory anyway) has a definition of "competence" when it comes to EICs.

How do you propose to carry out the necessary tests of the installation that are associated with certifying it?
 
visit your local MP and explain that the people employed to a do their job are not doing it but are still charging you for it. A private firm would be took to court by trading standards. Would be interesting to see what an MP would say.
 
How do you propose to carry out the necessary tests of the installation that are associated with certifying it?

We have a fluke 1651 at work that I have my eye on 4 the weekend :D
I could also 'borrow' the guy that normally uses it. He is qualified and competant. So the LABC would have to accept his certificate even if not endorsed by the NICEIC wouldn't they?
 
You need to discuss this with your colleague, and find out from him what he's prepared to do, and what he's prepared to sign. A full BS7671 Inspection & Testing Electrical Installation Certificate requires more than simply testing a circuit after installation.

But it certainly sounds like you've got the ingredients for a solution. Ask the Building Inspector what he would want regarding the electrics before he'll issue a completion certificate, remembering that there is no legal basis whatsoever on which he can insist that you use a NICEIC/NAPIT/ECA/UTCAA registered spark.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top